Frequently, there is a need to carry out such control with a high speed, sometimes also in line with the manufacture or mounting. The environmental conditions may be very difficult from a contamination point of view. Additionally, the type of material of the object or objects forming the joint may vary considerably and fall within the entire range from organic materials to inorganic materials or combinations of such materials.
Control systems are previously known for, for instance, weld joints in metal objects, where an energy rich radiation is used, for instance X-ray radiation, which in one way or the other penetrates the joints and gives an indication, for instance an X-ray image, of the actual condition. The "resolution capacity" of said system is strictly dependent on the type of material--basically, metal is the only type of material possible to use, at least at high speeds.
Previously, it has been especially difficult to examine the quality of joints formed in plastics material, especially when such examination has been carried out in an application where the joint defines a space containing an organic substance, for instance sealed closures or other sealing arrangements for food packages. Previously, the organic structure of the material forming the joint and the organic product enclosed inside the joint has caused problems when attempts were made to detect possible product residues in the joint.